"But then, through the darkness, fire erupted: crimson and gold, a ring of fire that surrounded the rock so that the Inferi holding Harry so tightly stumbled and faltered; they did not dare pass through the flames to get to the water. They dropped Harry; he hit the ground, slipped on the rock, and fell, grazing his arms, but scrambled back up, raising hiswand and staring around. Dumbledore was on his feet again, pale as any of the surrounding Inferi, but taller than any, too, the fire dancing in his eyes; his wand was raised like a torch and from its tip emanated the flames, like a vast lasso, encircling them all with warmth."

The Firestorm[3] is a charm that produces a large ring of fire around the caster, from his his/her wand.[1] When the caster moves, so the ring of flame will move with them in the same direction, swirling like a flaming lasso.[1] The caster may also shoot jets or balls of flame at individual targets or opponents while the fire is still being produced, which will inflict a small amount of damage to them.[2] The spellPartis Temporus will temporarily create a gap in the flames to allow safe passage through.[2]

Behind the scenes

In the book, the spell merely conjured a lasso of flames, like a rope made of fire. In the films, however, this was dramatised to have a wall of flame swirling around them, filling up most of the cave, with Dumbledore shooting fireballs at the Inferi underwater.

Due to the increased intensity in the film portrayal, on par with Fiendfyre, it is unknown whether Aguamenti or Aqua Eructo would work to extinguish the fire rope.

It is possible that the spell, as it appears in the book, is the Fire ropecharm, due to the novel's description of the fire as "a vast lasso" of flames produced from Dumbledore's wand.